Violence between shia and sunni goes back to the schism which initially was political and not religious. The hatred hasn't stopped and this gruesome act is just the latest atrocity.
The reports say that the extremists have links to or come from Pakistan. There the sectarian violence against Shia and other groups, eg Christians and Ahmadis, by extremist such as Lashkar-e-Jahgvi in this case and other extremists such as Khatme-Nabuwat is decades old. The reasons are many - but one of the main ones is the influence of the Mullahs and the corruption of the politicians.
The problem for eh is quite clear. Islamophobic bloggers and Islamophobes in general have to reconcile the fact that in the West the vast majority of terrorist atrocities are not carried out by Muslims or Jihadists. Indeed, in the EU last year less than 1% of the terror attacks were by Muslims and of those none were fatal.
Jihadist terror attacks in the West that are successful are actually outliers.
If the Islamophobic view of Muslims wanting to blow up westerners was true, you'd expect more attacks like Brievik's in Norway coming from Muslims. The Muslims in the West have the same access to the internet and materials as Brievik did. The Muslims in the East have the same access to materials and training that the extremists in Pakistan etc have that blow up fellow Muslims.
Therefore the low numbers of attacks in the West by Jihadists can't be down to lack of material or access to training (especially as Brievik got his info over the internet).
The only credible explanation of the low levels of attacks in the West is that there isn't this groundswell of Jihadists wanting to blow up Westerners. There is within the Muslim community a small percentage of Brievik and McVeigh wannabes, and so far thankfully they have come from the shallow end of the genepool and have proved to be incompetent. We won't continue to be so lucky though.
Now, this is more than just a theory - empirical evidence is there that the threat is overblown. Charles Kurzman's book: "The Missing Martyrs" covers exactly this point:
http://motherjones.com/mixed-media/2011 ... -jihadists Cheers,
Shafique